1. Field of the Invention
The present invention relates to a coulomb-type electrostatic chuck with a heater.
2. Description of Related Art
In manufacturing semiconductor devices and the like, a coulomb-type electrostatic chuck with a heater has hitherto been used. This electrostatic chuck with a heater includes a base made of ceramic. In the base, electrodes and a resistance heating element are disposed. The upper surface of the base is formed as a substrate holding surface on which a substrate such as a wafer is placed. Part of the base between the electrode and the substrate holding surface is formed as a dielectric layer, and another part between the electrode and the lower surface of the base is formed as a supporting member (for example, see Japanese Patent Laid-open Publication No. 11-12053).
However, in the aforementioned conventional electrostatic chuck with a heater, since the dielectric layer has a small volume resistivity, chucking and de-chucking response of a substrate placed on the substrate holding surface may be insufficient. The slower the chucking and de-chucking response of the substrate is, the longer it takes for the substrate to be separated from the electrostatic chuck. This increases processing time and reduces substrate processing capability per unit time.
Moreover, the main component of the resistance heating element is niobium (Nb), and the niobium may diffuse into the supporting member. The diffusion of the niobium increases resistance of the entire resistance heating element, and part of the resistance heating element from which the niobium component has diffused has a heat density different from a desired design value. Moreover, the diffusion degree of the niobium varies by location in the base, and the temperature distribution in the substrate holding surface is broadened, thus causing a problem of reduction in thermal uniformity of the substrate. Such reduction in thermal uniformity of the substrate makes it difficult to obtain uniform etching or film formation in a semiconductor-manufacturing process. The yield of manufactured devices may be therefore reduced.
Accordingly, an object of the present invention is to provide an electrostatic chuck with a heater in which the volume resistivity of the dielectric layer is increased to improve the chucking and de-chucking response of a substrate placed on the substrate holding surface and niobium as a main component of the resistance heating element is prevented from diffusing into the supporting member.
To achieve the aforementioned object, an electrostatic chuck with a heater according to the present invention includes: a base which is composed of a sintered body containing alumina; an electrode embedded in an upper part of the base: and a resistance heating element embedded in a lower part of the base, the base including a dielectric layer between the electrode and an upper surface of the base and a supporting member between the electrode and a lower surface of the base. The dielectric layer has a carbon content of not more than 100 ppm, and the supporting member has a carbon content of 0.03 to 0.25 wt %. Moreover, the resistance heating element is formed into a coil and mainly composed of niobium.
The electrostatic chuck with a heater according to the present invention has the following effects.
1) The carbon content of the supporting member is 0.03 to 0.25 wt %. It is therefore possible to prevent diffusion of niobium as a main component of the resistance heating element. By preventing the diffusion of the niobium component, the resistance heating element is allowed to have prescribed resistance, thus providing an effect on achieving heating density of a desired design value. Furthermore, the alumina sintered body of the supporting member is colored gray-black or black and efficiently radiates heat from the resistance heating element, thus providing an effect on an increase in heating efficiency. It is therefore possible to provide an effect on good thermal uniformity of the heated substrate.2) The resistance heating element is formed in a coil and embedded in the supporting member. Accordingly, part of the supporting member above the resistance heating element and part below the same are joined to each other more firmly than the case where a resistance heating element is composed of a thin film obtained by screen printing or the like. Moreover, the resistance heating element is formed into a coil and radiates heat three-dimensionally. Accordingly, the resistance heating element can transmit heat to the substrate holding surface more efficiently than the resistance heating element composed of a thin film obtained by screen printing or the like.3) The dielectric layer has a low carbon content of not more than 100 ppm and accordingly has high volume resistivity. When this electrostatic chuck is employed as a coulomb-type electrostatic chuck, the chucking and de-chucking response of a substrate placed on the substrate holding surface can be improved.4) The resistance heating element is mainly composed of niobium and has a thermal expansion coefficient close to that of the base containing alumina. Accordingly, it is possible to reduce thermal distortion occurring between the resistance heating element and part surrounding the same when the resistance heating element is heated. It is therefore possible to obtain an electrostatic chuck with a heater which has a long life; is resistant to failure; and has a high long-term reliability even after repeated heat cycles.